This invention relates to the driving of earth anchors into the earth, and in particular to an improved method and drive tool for driving medium duty earth anchors. Medium duty earth anchors have a number of uses in supporting and stabilizing static structures. Probably their most common use today is in anchoring mobile homes, although they are also used for anchoring or guying a wide variety of other structures.
A "medium duty earth anchor" includes a guy rod having a diameter of from about one-half to about three quarters inch and a length of from 3 to 5 feet, and a single turn helix, having a diameter from about 4 to about 8 inches, near the lower end of the rod.
The rod is typically made of carbon steel (0.20% to 0.40% carbon: SAE 1020 to 1040). The lower end of the rod is generally pointed and the head of the rod is provided with some sort of attachment means for attaching the anchor to a guy wire, strap or the like. The attachment means may be an eye or buckle or may simply be a screw thread or the like to which a fastener may be attached.
The helix is conventionally a sheet metal disc about one-eighth to three-sixteenths inches thick, having a radial split and being bent to form a single turn screw thread. The pitch of the helix, that is, the axial distance between the edges of the radial split, is from about 1 to 3 inches. The pitch of a 6 inch helix is typically about 13/4 inches at the guy rod and 2 inches at the circumference of the disc. The helix is typically spaced about 2 inches from the sharpened lower end of the guy rod. Some anchors include a second helix spaced perhaps 41/2 inches above the lower helix. The configuration of the helix may vary somewhat from that described, and is not critical to the present invention.
Medium duty anchors are well known and are commercially available from numerous manufacturers.
The installation of medium duty earth anchors has proven difficult. The anchors are too large for easy installation with a hand-held lever bar. The large, truck-mounted drilling equipment used for driving heavy-duty utility anchors, however, is also impractical; many jobs simply do not require installation of enough anchors to justify bringing in large equipment, and the space available frequently precludes its use.
In recent years hand-held electric drive tools have been used for driving medium-duty anchors. For the most part, these tools have been pipe threaders equipped with special adapters for driving earth anchors. These drivers include the usual horizontal handle and horizontal universal (AC-DC) motor. The motor drives a worm which in turn drives a ring gear. As is well known, the universal motor has a high shaft speed, 3500 rpm or more, which is reduced by the gearing to a ring gear speed of from about 14 to 26 rpm. The motor may be from about 1/2 to 1 horsepower. A slip-through adapter in the ring gear converts the pipe threader to an anchor driver. The adapter may engage the head of the anchor or may be of the type which extends the length of the anchor rod and drives the upper edge of the disc itself. The adaptation of the pipe threader may also include the addition of a second handle, for two-man operation.
Although such electric drive tools are in general use today, they are a far from satisfactory approach to driving medium duty anchors. The anchor frequently strikes obstructions in the ground, such as rocks and roots, and often hangs up on them. When it does, the shock throws the operators off balance and sometimes causes them injuries. When the anchor hangs up, it must be backed out a way and driven again, in hopes of missing the obstruction. Many times, the anchor must be extracted and started anew, or a new anchor used if the first is bent beyond use. Although anchors driven by prior anchor driving means occasionally cut through obstructions on which they hang up, this is not always advantageous as when the obstruction is a buried pipe or electrical cable.
Another problem with previously known electric anchor drivers has been their extremely short life. The gears are stripped or the motor is burned out with discouraging regularity.
A number of governmental agencies have specified minimum holding power for mobile home anchors. The specifications have not always been met with prior driving tools when the soil has provided less than perfect holding qualities.